clippy_lints/src/question_mark.rs

   1 use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   2 use crate::rustc::{declare_tool_lint, lint_array};
   3 use if_chain::if_chain;
   4 use crate::rustc::hir::*;
   5 use crate::rustc::hir::def::Def;
   6 use crate::utils::sugg::Sugg;
   7 use crate::syntax::ptr::P;
   8
   9 use crate::utils::{match_def_path, match_type, span_lint_and_then};
  10 use crate::utils::paths::*;
  11 use crate::rustc_errors::Applicability;
  12
  13 /// **What it does:** Checks for expressions that could be replaced by the question mark operator
  14 ///
  15 /// **Why is this bad?** Question mark usage is more idiomatic
  16 ///
  17 /// **Known problems:** None
  18 ///
  19 /// **Example:**
  20 /// ```rust
  21 /// if option.is_none() {
  22 ///     return None;
  23 /// }
  24 /// ```
  25 ///
  26 /// Could be written:
  27 ///
  28 /// ```rust
  29 /// option?;
  30 /// ```
  31 declare_clippy_lint!{
  32     pub QUESTION_MARK,
  33     style,
  34     "checks for expressions that could be replaced by the question mark operator"
  35 }
  36
  37 #[derive(Copy, Clone)]
  38 pub struct QuestionMarkPass;
  39
  40 impl LintPass for QuestionMarkPass {
  41     fn get_lints(&self) -> LintArray {
  42         lint_array!(QUESTION_MARK)
  43     }
  44 }
  45
  46 impl QuestionMarkPass {
  47     /// Check if the given expression on the given context matches the following structure:
  48     ///
  49     /// ```ignore
  50     /// if option.is_none() {
  51     ///    return None;
  52     /// }
  53     /// ```
  54     ///
  55     /// If it matches, it will suggest to use the question mark operator instead
  56     fn check_is_none_and_early_return_none(cx: &LateContext<'_, '_>, expr: &Expr) {
  57         if_chain! {
  58             if let ExprKind::If(ref if_expr, ref body, _) = expr.node;
  59             if let ExprKind::MethodCall(ref segment, _, ref args) = if_expr.node;
  60             if segment.ident.name == "is_none";
  61             if Self::expression_returns_none(cx, body);
  62             if let Some(subject) = args.get(0);
  63             if Self::is_option(cx, subject);
  64
  65             then {
  66                 span_lint_and_then(
  67                     cx,
  68                     QUESTION_MARK,
  69                     expr.span,
  70                     "this block may be rewritten with the `?` operator",
  71                     |db| {
  72                         let receiver_str = &Sugg::hir(cx, subject, "..");
  73
  74                         db.span_suggestion_with_applicability(
  75                             expr.span,
  76                             "replace_it_with",
  77                             format!("{}?;", receiver_str),
  78                             Applicability::Unspecified,
  79                         );
  80                     }
  81                 )
  82             }
  83         }
  84     }
  85
  86     fn is_option(cx: &LateContext<'_, '_>, expression: &Expr) -> bool {
  87         let expr_ty = cx.tables.expr_ty(expression);
  88
  89         match_type(cx, expr_ty, &OPTION)
  90     }
  91
  92     fn expression_returns_none(cx: &LateContext<'_, '_>, expression: &Expr) -> bool {
  93         match expression.node {
  94             ExprKind::Block(ref block, _) => {
  95                 if let Some(return_expression) = Self::return_expression(block) {
  96                     return Self::expression_returns_none(cx, &return_expression);
  97                 }
  98
  99                 false
 100             },
 101             ExprKind::Ret(Some(ref expr)) => {
 102                 Self::expression_returns_none(cx, expr)
 103             },
 104             ExprKind::Path(ref qp) => {
 105                 if let Def::VariantCtor(def_id, _) = cx.tables.qpath_def(qp, expression.hir_id) {
 106                     return match_def_path(cx.tcx, def_id,  &OPTION_NONE);
 107                 }
 108
 109                 false
 110             },
 111             _ => false
 112         }
 113     }
 114
 115     fn return_expression(block: &Block) -> Option<P<Expr>> {
 116         // Check if last expression is a return statement. Then, return the expression
 117         if_chain! {
 118             if block.stmts.len() == 1;
 119             if let Some(expr) = block.stmts.iter().last();
 120             if let StmtKind::Semi(ref expr, _) = expr.node;
 121             if let ExprKind::Ret(ref ret_expr) = expr.node;
 122             if let &Some(ref ret_expr) = ret_expr;
 123
 124             then {
 125                 return Some(ret_expr.clone());
 126             }
 127         }
 128
 129         // Check if the block has an implicit return expression
 130         if let Some(ref ret_expr) = block.expr {
 131             return Some(ret_expr.clone());
 132         }
 133
 134         None
 135     }
 136 }
 137
 138 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for QuestionMarkPass {
 139     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
 140         Self::check_is_none_and_early_return_none(cx, expr);
 141     }
 142 }